Theo Verelst Model Airship Page

A fusion between hot air balloons, helium filled zeppelins (bimps),
and model aircrafts.A bit of an article-wise text, scroll down to see the fun parts:pictures and later on video captures of the flying prototypes.

Introduction.

From the early days of aviation onward, there has been a major seperation
between propelled airplanes, using a wing or direct vertical lift, and
balloons, which have intrinsic lift. The only bridge beween that seperation
has been the airship, or zeppelin, or blimp, and it has been discarded
for major aviation purposes, and even in the model world, it has recieved
little attention.

In this text we will look into the possibilities of (helium) airships
on a small scale, that is maybe up to cargo capacities of 100kg, and mainly
in the less than 1KG equivalent lift range.

We will assess the possibilities of such a model airship, its potential,
practical feasibility, and even present working prototypes that proof that
all associated problems can be solved to arrive at a working model airship
with high flexibility, at very acceptable cost, and with ample flying capacities.

Since the prototypes are realy that: prototypes, some assessment of
the encountered idiosyncrasies will result in some major models of the
physics and flying properties of the proposed types of models, enough to
start building some more developed prototypes.

Please mind that even though the prototypes were done a a budget of
maybe a hundred dollars, the efforts are seriously aimed at airships that
can compete with model choppers and aircrafts for their flying capabilities,
and beat them in some, such as the time of flight, manouverability, and
safety. It is very reasonable to expect research in some of the proposed
directions to yield interesting results that have a variety of applications.

Historical considerations.

Balloons and blimps are an interesting form of aviation, that may have
been hampered by at least one or more of the following reasons:

it is expensive to built an airship big enough to carry serious loads

the lift control possibilities are limited and less straightforward as
with other aircrafts

helium is no too cheap, and can not easily be contained in a 100% airtight
manner

the size of airships make them wind sensitive

the safety of passengers depends on the quality of the gass enclosure

due to their size, flight speeds are limited

The remainder of this text makes clear that some of these limitations don't
apply to model airships, others can easily be lifted or made irrelevant,
and others are not decisive to conclude that model airships are not feasible.

Big airships, about 200 meters long, ar still around, and can be rented
for about $300,000,= a month, which shows that at least there is some interest,
and it is easy to understand that the comfort of a hot air balloon (completely
silent flight), combined with far greater action radius (in the desired
direction !) gives then a competative edge.

Hot air balloons have developed into a relatively safe form of aviation,
and can already be enjoyed for prices around $200 per person.

Blimps are mainly a promotional gimmic, and usually not seen as aircrafts,
but as static attention drawers.

Physical figures.

A balloon filled with helium, such as latex weather ballons or party balloons,
can carry around 1.6 KG of load per cubic meter (1000 liters) of (at 1+epsilon
bar of pressure, epsilon<0.1) helium volume, which is a roundish balloon
with a diameter of about 1.5 meters. Of course this depends on: surrounding
air pressure, temperature, and balloon thickness and stretchability.

The balloons themselves, the ones that I bought are latex balloons of
the party type, costing around $10 a piece, depending on size weigh in
the order of 50 grams, so when it is filled with helium it has zero lift
at a diameter of about 30cm, and starts to increase lift with every liter
of helium that it is filled with.

Helium costs me about 1-2 dollar cents per liter, in quantities from
1000 to 10,000 liters, excluding the deposit of $125 for the gas container,
and $0.50 a day container rent after 1 days.

A remote control receiver weighs a few dozen or so grams, baby-cell
rechargeable batteries weigh 25 grams each, delivering 600mAmp.h at 1.2
Volts, and servo control units (actuators) can weigh as little as 20 grams,
the ones that I bought weigh around 40 grams.

A 2 channel remote control unit, transmitter, receiver, 2 servos, and
battery container, with a range of at least 300 meters (40MHz band) cost
me around $60,-, and it should be mentioned that the supplied receiver
and servos nicely adhere to model remote control standards and can easily
be fed by a custom pulse control signal, for instance to drive the height-control
servo by a altitude sensor, in feedback fashion.

Model airship proposal: outline of the major properties.

Considering a balloon can easily carry half a kilogram or so of extra materials,

Highlighted feature: lift/altitude control

Prototypes!

Observed model properties.

The latex helium balloons loose their helium slowly, but when the larger
(thicker) balloons ar enot filled to their specified size, they keep the
gas fairly well, a week or so of usefull lift without refil is reasonably
possible.

The two balloon prototype with propulsion in the middle, under the balloons
reponds to rudder motions as can be expected: the longitudinal directional
stability is poor, which means that the redirected air flow along the rudder
will result in a torsion on the whole balloon system, which is than accelerated
to turn, and needs to be accelarated into stable forward flight by equivalent
counter rudder. Since the amount of forward thrust from one cell is nice
to make the model fly at moderate walking speed, it is nt enough to auto-stabalize
the model in forward direction, so a rudder motion is often followed by
sideway drift that is not easily compensated for, due to the large momentum
(as result of the total weight) and the relatively smal compensating force
from the propellors forward thrust. At higher flying speeds, this should
be better, now the balloons' travelling speed is also not too limited by
the forward thrust of the propellor, it simply doesn't develop a very high
overall air speed. (Its a 5volt 140mA idle current motor, running at 1.2
V, with a 12 cm nylon prop).